"Umarov rose to prominence in the 2000s alongside notorious terrorist leaders such as Shamil Basayev, a fellow Chechen, but also radicalized jihadis from places like Jordan or Saudi Arabia with names like al-Khattab, Abu Hafs, and Abu Walid.

"The presence of these foreign fighters helped turn the Chechen fight from a secular, ethnic-based independence cause towards a pan-Islamist, cross-border movement that spilled into other parts of the Caucasus.

"In 2007, after Russian forces killed a series of top commanders including Basayev and gained the upper hand in Chechnya, the insurgency began to fracture. Umarov declared himself "emir of the Caucasus Emirate," an umbrella of rebel groups through the North Caucasus. Umarov used suicide bombers — which Basayev had helped introduce to Russia earlier that decade — in incidents like the 2002 Moscow theater siege, and the 2004 seizure of a school in Beslan."